This application claims the priority of German Application No. 196 30 870.4, the disclosure of which is expressly incorporated by reference herein.
The invention relates to a process for aiding a starting movement of a vehicle from a standstill.
It is known that problems occur when starting movement of a vehicle on an incline such as a hill, particularly in a vehicle having a manual transmission. The vehicle operator must, for example, release the foot brake pedal in order to be able to operate the accelerator pedal and thus be able to provide an engine torque required for the starting operation. This sometimes presents problems. Only experienced and skillful vehicle operators can use the mechanical parking brake for this type of starting without any problems. The starting operation becomes the more difficult the steeper the slope.
Particularly when attempting to start movement of the vehicle while on an incline, the vehicle frequently rolls rearward and endangers other traffic participants.
It is an object of the invention to provide a process for aiding a starting movement of a vehicle from a standstill which makes it possible for the user to start movement of the vehicle without any problems in a simple, uncomplicated and effective manner as well as in any position of the vehicle.
This and other objects have been achieved according to the present invention by providing a process for aiding a starting movement of a vehicle from a stopped position, comprising the steps of: maintaining a brake pressure via a braking control input independent of a vehicle operator braking input in order to maintain the vehicle in the stopped position; sensing an engine torque generated by an engine of the vehicle; and terminating the maintaining step when the engine torque exceeds a limit value.
This and other objects have also been achieved according to the present invention by providing a process for aiding a starting movement of a vehicle from a stopped position, comprising the steps of: sensing a torque generated by an engine of the vehicle; and sensing a velocity of the vehicle; and when the velocity is zero, further comprising the steps of: determining a brake pressure value required to maintain the velocity of zero; maintaining the brake pressure value via a braking control input independent of a vehicle operator braking input; and terminating the maintaining step when the engine torque exceeds a limit value.
This and other objects have also been achieved according to the present invention by providing a system for aiding a starting movement of a vehicle from a stopped position, comprising: a control unit operably connected to a brake system of the vehicle; a velocity sensor which senses a velocity of the vehicle; a torque sensor which senses a torque generated by an engine of the vehicle; and a brake pressure sensor which senses a brake pressure in the brake system, wherein when the velocity sensor senses a velocity of zero, the control unit (a) determines a brake pressure value required to maintain the vehicle at the velocity of zero, (b) controls the brake system to maintain the brake pressure value, and (c) terminates maintaining the brake pressure value when the engine torque exceeds a limit value.
In modern vehicles, the operation of the wheel brakes is increasingly possible not only via the foot brake pedal but also via additional, so-called secondary brake circuits. Particularly in extreme driving situations, it is beneficial, for example, to protect the vehicle occupants and other participants in traffic via braking interventions conducted by an additional braking system independent of the driver-controlled foot brake which additional braking system is controlled as a function of sensed operating conditions of the vehicle.
In the case of the known anti-slip control or anti-lock braking systems, or vehicle stability control or traction control systems, this takes place by operating the vehicle brakes by means of an external power or secondary brake circuit. For this purpose, the vehicle brakes can be selectively uncoupled from the primary brake circuit (master brake cylinder controlled by the vehicle operator via the foot brake pedal) and can be acted upon by brake pressure from the secondary brake circuit via a pump/valves. This pressure admission may be independent of the position of the brake pedal. For generating the required brake pressure at the individual wheels by means of an external power or secondary brake circuit, the above-mentioned pump is therefore used and not the foot power of the vehicle operator. This is therefore a braking intervention by way of an external power, in which case there may be a superimposition of foot power and external power.
The present invention utilizes the concept of controlling the brake operation via an external power or secondary brake circuit independent of the foot brake input of the vehicle driver. In a first step of the process according to the invention, a braking intervention by means of an external power or an secondary brake circuit takes place when the vehicle is at a standstill, whereby the rest condition of the vehicle can be ensured. For this purpose, the required brake pressure is either (a) built up by the secondary brake circuit by generating an external power and then held by means of valves, or (b) if the vehicle operator has already provided the required brake pressure by operating the brake pedal, the brake pressure is maintained by means of valves. Thus, the standstill of the vehicle can also be ensured even when the brake pedal is not operated. The power generated by the driving engine of the vehicle or the corresponding engine torque will then be continuously sensed. If this engine torque exceeds a certain predetermined threshold value, the braking intervention which is continuously produced by means of the external power is terminated. The engine torque generated by the engine will exceed the predetermined limit value when the vehicle operator operates the accelerator pedal beyond a certain point. In the process according to the invention, as a result of the operation of the accelerator pedal, an intended starting operation is therefore recognized and when a certain engine torque is provided so that, for example, during a starting operation on a hill, a rearward rolling movement of the vehicle is prevented.
According to certain preferred embodiments of the present invention, the braking intervention by means of the external power does not take place before predetermined conditions exist. Such operating conditions may, for example, be the vehicle speed, a clutch switch, an engine operating signal and/or another activating switch.
Since, at the start of the braking intervention, the vehicle may not yet have completely reached a standstill, the pressure buildup preferably takes place slowly at the start of the braking intervention, particularly as a function of the vehicle speed and/or of time. This prevents a jerky stop and ensures a smooth slowing movement until the vehicle has come to a complete rest.
According to certain preferred embodiments of the present invention, the limit value at which the braking intervention by means of external power is completed corresponds to the power which is minimally necessary for ensuring the stoppage of the vehicle. One way of determining such a reference value consists of taking into account the brake pressure which exists at the point in time at which the vehicle speed has just reached zero. Naturally, vehicle-specific or environment-specific parameters may also be taken into account when determining such a reference value. Such data are, for example, the transmission ratio or the design for the first gear or the engagement of the reverse gear. With respect to environment-specific parameters, there is, for example, the vehicle tilt (slope, gradient) which can be determined, for example, from the anti-theft system or the analysis of the filling level of the tank.
In order to ensure a smooth starting movement, at the conclusion of the braking intervention, the brake pressure is preferably uniformly reduced corresponding to a predetermined course. In this case, it is advantageous to differentiate between an uphill start and a downhill start because a fast or slow release of the brake may be necessary as a function thereof. For this purpose, preferably the position of the gear selector lever as well as the information concerning the slope (e.g., directly as an angle-of-tilt sensor of the anti-theft warning system or of the analysis system of the tank filling level indicator) is utilized.
According to further preferred embodiments, a temperature compensation takes place in the case of a brake disk cooling. For this purpose, for example, a corresponding pretensioning can be given in the case of the brake operation. The higher pretensioning is taken into account during the release function by advancing the release operation. However, the temperature can also be taken into account or compensated by way of an aftertensioning operation while taking into account the rotational wheel speeds or a separate temperature model which determines and indicates the temperature.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.